The use of slide transparencies has in recent years become increasingly popular, particularly in the field of visual communications. Those involved in the dissemination of ideas for such purposes as educational courses and business, professional and governmental seminars are continually seeking new ways to present information visually. One of the most convenient and readily available techniques for such presentation involves the use of standard 35 mm slide transparencies. For maximum utilization of such slide transparencies a simple and convenient method must be available for reproducing various printed materials as projectable images on slide transparencies.
While silver halide and diazo film have been used in making such slide transparencies, the imaging and developing processes for such film are generally time consuming and require trained operators. On the other hand, electrophotography while capable of producing excellent high resolution images in a convenient and economical manner, lacks effective methods and means for utilizing electrophotographic film in slide transparencies projectable in 35 mm projectors.
The only commercially available electrophotographic slide processing system employs fully mounted slide frames. These frames consist of a film laminated between two window apertured paperboard frames, the plane of the film being recessed inwardly of the outer surface of the frames. A hole is provided through one of the frames for contact with the photoconductive layer of the film. In the use of these slides some imaging deficiencies have been encountered, particularly along the outer edges of the film adjacent the window edge of the frame. It is believed this difficulty results from the surface tension of the liquid toner which is applied at the toning head of the slide processor system. Inasmuch as the outer surfaces of the frame and film are not coplanar, there is a tendency due to surface tension for the toner to bridge areas of the film adjacent the edges of the frame. Attempts to alleviate this problem have involved the use of paperboard frames sufficiently absorbent to wick up the toner liquid so that the full imaging potential of the film area is utilized. Unfortunately, the frames remain wet or damp as they emerge from the processor unit and tend to warp on drying. As a consequence, it has been the practice to make these frames considerably thicker than the standard 35 mm photographic slide used in the most commercially popular slide projectors, thereby mandating the use of less popular slide projectors or projectors especially adapted for use with these particular slide frames.
Furthermore, this non-coplanar configuration of such prior art slides renders it inconvenient if not impossible to place such slides in surface-to-surface contact with other photographic films such as silver halide or diazo films. Such surface-to-surface contact is desirable for example in the reproduction of an electrophotographic film image onto another type of film or in the superpositioning and simultaneous projection of an electrophotographic film image and a second background image.
It is the principal object of this invention to provide slide transparencies constructed for use in an electrophotographic slide processor which overcome the drawbacks of commercially available slide transparencies.
Another object of this invention is to provide slide transparencies of open frame construction wherein the electrophotographic film provides a wholly planar surface for imaging and toning.
It is a further object of this invention to provide slide transparencies of the above type wherein the planar processing surface is provided with a fully exposed electrically conductive layer.
Yet another object of this invention is to provide a slide transparency frame construction which lends itself to efficient and economical manufacturing procedures, each of use in a slide processor unit and after processing is readily converted to a fully mounted slide frame for projection in standard 35 mm slide projectors.
A further object of the present invention is to provide such a slide transparency which can be assembled without heat sealing.
It is another object of the present invention to provide a slide transparency of the above type wherein the transparency image may be conveniently contact duplicated onto another photographic film such as a diazo or silver halide color film.
It is yet a further object to provide a slide transparency in which images on a pair of film surfaces are disposed in superposed registration with one another for simultaneous projection of a composite image.